Apple's iOS App Store suffers first major attack

Apple Inc said on Sunday it is cleaning up its iOS App Store to remove malicious iPhone and iPad programs identified in the first large-scale attack on the popular mobile software outlet.

The company disclosed the effort after several cyber security firms reported finding a malicious program dubbed XcodeGhost that was embedded in hundreds of legitimate apps.

It is the first reported case of large numbers of malicious software programs making their way past Apple's stringent app review process. Prior to this attack, a total of just five malicious apps had ever been found in the App Store, according to cyber security firm Palo Alto Networks Inc.

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Apple event, September 9

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Apple's iOS App Store suffers first major attack

Employees assist attendees in front of the Bill Graham Civic Auditorium before the start of an Apple Inc. product announcement in San Francisco, California, U.S., on Wednesday, Sept. 9, 2015. Apple is expected to unveil its iPhone 6s and 6s Plus, as well as an updated version of its Apple TV set-top box. Photographer: Michael Short/Bloomberg via Getty Images

SAN FRANCISCO, CA - SEPTEMBER 9: Apple CEO Tim Cook waves as he arrives on stage during an Apple Special Event on at Bill Graham Civic Auditorium September 9, 2015 in San Francisco, California. Apple Inc is expected to unveil latest iterations of its smart phone, forecasted to be the 6S and 6S Plus. The tech giant is also rumored to be planning to announce an update to its Apple TV set-top box. (Photo by Stephen Lam/ Getty Images)

SAN FRANCISCO, CA - SEPTEMBER 9: Apple CEO Tim Cook waves as he arrive on stage during an Apple Special Event on at Bill Graham Civic Auditorium September 9, 2015 in San Francisco, California. Apple Inc is expected to unveil latest iterations of its smart phone, forecasted to be the 6S and 6S Plus. The tech giant is also rumored to be planning to announce an update to its Apple TV set-top box. (Photo by Stephen Lam/ Getty Images)

Jeff Williams, senior vice president of operations for Apple Inc., speaks during an Apple product announcement in San Francisco, California, U.S., on Wednesday, Sept. 9, 2015. Apple Inc. is expected to unveil its iPhone 6s and 6s Plus, as well as an updated version of its Apple TV set-top box. Photographer: David Paul Morris/Bloomberg via Getty Images

Tim Cook, chief executive officer of Apple Inc., speaks during an Apple product announcement in San Francisco, California, U.S., on Wednesday, Sept. 9, 2015. Apple Inc. is expected to unveil its iPhone 6s and 6s Plus, as well as an updated version of its Apple TV set-top box. Photographer: David Paul Morris/Bloomberg via Getty Images

SAN FRANCISCO, CA - SEPTEMBER 9: Apple Senior Vice President of Worldwide Marketing Phil Schiller speaks about the prices for iPad Pro on stage during a Special Event at Bill Graham Civic Auditorium September 9, 2015 in San Francisco, California. Apple Inc. is expected to unveil latest iterations of its smart phone, forecasted to be the 6S and 6S Plus. The tech giant is also rumored to be planning to announce an update to its Apple TV set-top box. (Photo by Stephen Lam/ Getty Images)

SAN FRANCISCO, CA - SEPTEMBER 9: Apple Senior Vice President of Worldwide Marketing Phil Schiller speaks about the prices for iPads on stage during a Special Event at Bill Graham Civic Auditorium September 9, 2015 in San Francisco, California. Apple Inc. is expected to unveil latest iterations of its smart phone, forecasted to be the 6S and 6S Plus. The tech giant is also rumored to be planning to announce an update to its Apple TV set-top box. (Photo by Stephen Lam/ Getty Images)

Apple TV is demonstrated during the Apple Inc. product announcement in San Francisco, California, U.S., on Wednesday, Sept. 9, 2015. Apple Inc. introduced a larger iPad with a 12.9-inch screen, designed to attract business users and jump-start demand for its tablets. Photographer: David Paul Morris/Bloomberg via Getty Images

Philip 'Phil' Schiller, senior vice president of worldwide marketing at Apple Inc., speaks during an Apple product announcement in San Francisco, California, U.S., on Wednesday, Sept. 9, 2015. Apple Inc. introduced a larger iPad with a 12.9-inch screen, designed to attract business users and jump-start demand for its tablets. Photographer: David Paul Morris/Bloomberg via Getty Images

Philip 'Phil' Schiller, senior vice president of worldwide marketing at Apple Inc., speaks during an Apple product announcement in San Francisco, California, U.S., on Wednesday, Sept. 9, 2015. Apple Inc. introduced a larger iPad with a 12.9-inch screen, designed to attract business users and jump-start demand for its tablets. Photographer: David Paul Morris/Bloomberg via Getty Images

Philip 'Phil' Schiller, senior vice president of worldwide marketing at Apple Inc., speaks about the Apple Inc. iPhone 6s and 6s Plus smartphones during an Apple product announcement in San Francisco, California, U.S., on Wednesday, Sept. 9, 2015. Apple Inc. introduced a larger iPad with a 12.9-inch screen, designed to attract business users and jump-start demand for its tablets. Photographer: David Paul Morris/Bloomberg via Getty Images

Tim Cook, chief executive officer of Apple Inc., speaks during an Apple product announcement in San Francisco, California, U.S., on Wednesday, Sept. 9, 2015. Apple Inc. introduced a larger iPad with a 12.9-inch screen, designed to attract business users and jump-start demand for its tablets. Photographer: David Paul Morris/Bloomberg via Getty Images

Attendees line up in front of the Bill Graham Civic Auditorium before the start of an Apple Inc. product announcement in San Francisco, California, U.S., on Wednesday, Sept. 9, 2015. Apple is expected to unveil its iPhone 6s and 6s Plus, as well as an updated version of its Apple TV set-top box. Photographer: David Paul Morris/Bloomberg via Getty Images

Credentials sit on a table in front of the Bill Graham Civic Auditorium before the start of an Apple Inc. product announcement in San Francisco, California, U.S., on Wednesday, Sept. 9, 2015. Apple is expected to unveil its iPhone 6s and 6s Plus, as well as an updated version of its Apple TV set-top box. Photographer: David Paul Morris/Bloomberg via Getty Images

Attendees line up in front of the Bill Graham Civic Auditorium before the start of an Apple Inc. product announcement in San Francisco, California, U.S., on Wednesday, Sept. 9, 2015. Apple is expected to unveil its iPhone 6s and 6s Plus, as well as an updated version of its Apple TV set-top box. Photographer: Michael Short/Bloomberg via Getty Images

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The hackers embedded the malicious code in these apps by convincing developers of legitimate software to use a tainted, counterfeit version of Apple's software for creating iOS and Mac apps, which is known as Xcode, Apple said.

"We've removed the apps from the App Store that we know have been created with this counterfeit software," Apple spokeswoman Christine Monaghan said in an email. "We are working with the developers to make sure they're using the proper version of Xcode to rebuild their apps."

She did not say what steps iPhone and iPad users could take to determine whether their devices were infected.

Palo Alto Networks Director of Threat Intelligence Ryan Olson said the malware had limited functionality and his firm had uncovered no examples of data theft or other harm as a result of the attack.

Still, he said it was "a pretty big deal" because it showed that the App Store could be compromised if hackers infected machines of software developers writing legitimate apps. Other attackers may copy that approach, which is hard to defend against, he said.